The present invention relates to a driving equipment for multi-gradation level reproduction which is used with a facsimile receiver, a printer, a light emitting display and so forth, and more particularly to a driving equipment for driving recording elements or displaying elements so as to perform not monochrome bilevel but gray scale recording.
In thermal recording employed in facsimile, since it requires a relatively long recording time of 2 to 5 msec/dot, a serial picture signal is converted into parallel signals, which are simultaneously applied as many parallel outputs to recording elements. For gray scale recording, too, such a serial-parallel conversion is needed. Driving equipments for such gray scale recording or display have been proposed in U.S. Pat. No. 4,074,319, "Light Emitting Diode Array Imaging System-Parallel Approach" issued on Feb. 14, 1978 and in U.S. Pat. No. 4,071,849, "System for Printing Images Having A Halftone" issued on Jan. 31, 1978. In the driving equipment disclosed in the former, an input picture signal is converted, for each picture element, into a signal having a plurality of pulses corresponding in number to the gradation level of the picture element and the converted signal is written in a multi-tap shift register. When a predetermined number of picture elements have been written, the shift register is read out at a low speed to derive therefrom at each tap an output which is supplied to a corresponding light emitting diode (LED) of an LED array. In this way, one picture element signal is rendered into pulses corresponding in number to the gradation level of the picture element signal. The larger the number of pulses is, the more the quantity of light emitted by the LED supplied with the picture element signal increases. Accordingly, the LED array provides a display having gray levels and, in addition, a plurality of picture element signals are applied in parallel to the LED array. This equipment requires a very large number of elements in the shift register for the serial-parallel conversion, and hence is not practical for recording or displaying a facsimile signal. Further, this equipment requires much time for changing the number of gradation levels per picture element and the number of picture elements to be applied in parallel to the LED array, and hence it is of limited application.
In the equipment set forth in the latter U.S. patent, an input picture signal is converted, for each picture element, into parallel codes of a plurality of bits, each corresponding to the gradation level of the picture element and the respective bits of the codes are written in parallel in a plurality of shift registers. When the bits have been written in the shift registers to their full capacity, the shift registers are simultaneously read out and the output codes are each written in a serial-parallel converting shift register, as a binary signal indicating whether each code is larger or smaller than a predetermined value. Upon each completion of reading out of the shift registers, the predetermined value is increased and the same operation is repeated. The parallel outputs from the serial-parallel converting shift register are simultaneously applied to corresponding recording elements. This equipment also requires a relatively large number of constituent elements and is not versatile in the modification of the number of gradation levels and the number of parallel outputs. Further, when the input signal is an analog signal, an expensive A-D converter is needed.
It is an object of the present invention to provide a driving equipment for multi-gradation level reproduction which has a small in the number of constituent elements and hence can be produced at low cost.
Another object of the present invention is to provide a driving equipment for multi-gradation level reproduction which permits easy modification of the number of gradation levels and the number of parallel outputs and hence is of wide application.
Yet another object of the present invention is to provide a driving equipment for multi-gradation level reproduction which has a small number of constituent elements and is highly universal in application and can be produced at low cost.